The caller, who campus officials said had a Middle Eastern accent, said the bombs would go off in 90 minutes. The call came into campus just before 8:45 a.m. local time. Those 90 minutes passed without incident, officials say.

Campus officials say that while activities at the school will resume at 5 p.m., all classes for the remainder of Friday have been canceled.

The University of Texas' website, www.utexas.edu, currently directs to an emergency information page telling everyone on campus to immediately evacuate all buildings and get as far away from campus as possible.

The school's official Twitter account (@UTAustin) also advised the campus community to evacuate the campus.

Evacuation due to threats on campus immediately evacuate all buildings get as far away from the buildings as possible. More to come.

Most students appeared to be leaving campus in an orderly and calm manner. Police blocked off roads to the 50,000-student campus as lines and lines of cars sat in gridlock trying to get out.

By 10:30 a.m., the university issued another advisory saying that buildings were still being checked and that no decision had been made on whether the campus would reopen for afternoon classes.

Ashley Moran, a freshman from Houston, said she was waiting to get into class when word quickly began spreading among students to leave immediately. She described the evacuation as "orderly but tense."

"It makes me really nervous I just know we're supposed to get out," she said.